1. Field of the Invention
This invention relates to decontaminating materials, including but not limited to liquids, sludges and soil. In one aspect this invention is directed to removing vaporizable organic contaminants from material. In another aspect this invention is directed to such processes and apparatuses for providing a relatively hot environment for such removal, and such processes in which heat is used efficiently and effectively.
2. Description of Related Art
Materials such as sludges and natural soil have been contaminated with toxic and dangerous materials such as gasoline, chemicals, diesel oil, cleaning solvents and the like. The presence of these contaminants results in environmental and health hazards. Many organic liquids that contaminate soils are toxic and carcinogenic and find their way into drinking water formations from contaminated soils. Organic contaminants from contaminated soil enter waterways and pollute and contaminate them, endangering human beings and killing fish and wildlife.
In my previous patent, U.S. Pat. No. 5,117,771 entitled "Method And Apparatus To Decontaminate Soil," incorporated fully herein by reference, I disclosed a method and apparatus for decontaminating soil. This invention did not provide for the removal of water from sludges, nor did it provide heat sufficient to remove liquids and certain contaminants from sludges. This invention did not provide for vaporized contaminant gases to be "swept" from a heating chamber. This invention could not be used at desired higher temperatures since it provided heat transfer fluids that could only be heated to about seven hundred degrees Fahrenheit and it did not use waste heat effectively. The invention included a method and apparatus for decontaminating soil that has been contaminated with vaporizable contaminants in which contaminated soil is conveyed through a treatment vessel by means of an auger with internal passages with a hot heat transfer fluid flowing through them. As the contaminated soil passes through the treatment vessel, it is heated to a point where the contaminants are vaporized and are withdrawn from the treatment vessel. Air is added to the interior of the treatment vessel from the atmosphere to lower the temperature of vaporized gases, but not to lower the temperature to such a point that the gases condense. Such condensation adversely affects downstream filtration efforts, e.g. resulting in undesirable coating of filter bags. Control means control the amount of air added to the treatment vessel to ensure that the oxygen level in the mixture of vaporized contaminates and air does not fall within a flammable or explosive range. Following the vaporization of the contaminates from the soil, the treated soil is removed from the treatment vessel.
Other prior art attempts to decontaminate soil that is contaminated with vaporizable contaminants include various types of solvent extraction of washing procedures utilized in an attempt to wash the contaminants from the soil. These attempts are costly, and have not been overly successful in removing such contaminants from soil. Other methods have involved heating soil in an attempt to vaporize the contaminants and drive the contaminants from the soil. Heating processes that employ heated kilns have not been too successful because of poor heat transfer, the tendency of moist soils to "ball up", dust formation and the like.
U.S. Pat. No. 4,738,206 discloses a method and apparatus for utilizing a heating vessel with a heated screw conveyor to heat soil as it is moved through the vessel to "vapor strip" contaminants from the soil. This method and apparatus have several problems. The method and apparatus provide for the exclusion of oxygen or air inside the heated stripping chamber which poses severe operating problems and requires that air locks or seals in other apparatus be utilized to rigorously exclude the entry of air into the heated chamber.
There has long been a need for efficient and effective methods and apparatuses for decontaminating material. There has long been a need for such methods and apparatuses which can employ relatively high temperatures. There has long been a need for such methods and apparatuses which can be used to decontaminate sludges as well as soils. There has long been a need for such methods and apparatuses which do not waste heat produced during operation.